1. Field of the Invention
This invention relates to a sieve or filter plate having a number of perforated or slotted areas. More specifically, this invention relates to such a plate in which relatively broad grooves are formed in the downstream side and the remaining floor or membrane is pierced by slots or perforations. The upstream side of the screen therefore only sees the slots or perforations, and because the membrane is thin, there is little chance for the slurry or mixture being filtered to become lodged in the plate and clog it up.
The process includes the step of forming the grooves on a plate, cutting the openings, by laser or other means, and, in some cases, squeezing the plate to flow material into the openings to make the openings more fine.
2. Description of the Prior Art including Disclosure Statement under .sctn..sctn.1.97 and 1.99
Sieve and filter elements are used in various industries, mainly in chemical and petrochemical plants, in paper and pulp mills and in the food and pharmaceutical industries and machinery.
Traditionally, the sieve elements consist of wire mesh screens, simple perforated and slotted sieve plates or fibre-based filter or screen elements. The known disadvantages in the existing machines are easy clogging and high pressure drop while pumping. Additional disadvantages are the wear and tear of the elements and contamination of the industrial process.
It is old to form perforations in filter plate by having the sides of the perforations diverge toward the downstream side of the plate. An example is disclosed in U.S. Pat. No. 4,317,023 which issed Feb. 23, 1982 to Gregory A. Gryskiewicz.
Further, it is old to squeeze a perforate sheet to reduce the pore size. This is disclosed, for instance, in the U.S. Pat. 3,049,796 which issued Aug. 21, 1962 to David B. Pall.